In hydrocarbon drilling operations, a blowout preventer (“BOP”) is used to form a pressure-tight seal at the top of a well and prevent the escape of formation fluids. A ram BOP achieves pressure control through the operation of hydraulically operated ram blocks. The ram blocks are grouped in opposing pairs and are forced together as a result of the hydraulic operation. Certain types of ram BOPs employ ram blocks designed to shear through pipe in the wellbore (e.g., drillpipe, a liner, or a casing string), hang the pipe off on the ram blocks, and seal the wellbore. Each ram block may include a ram packer designed to form a seal when the ram blocks are brought together. The ram blocks may each have arms that extend in towards the wellbore such that when the ram blocks are brought together, the ram arms mate in a way the resists upward deflection of the ram blocks due to well pressure.
When the ram blocks are brought together to shear a pipe in the wellbore, the pipe has a tendency to flatten before being sheared, effectively increasing the diameter of the pipe. Certain pipes may experience more flattening before being sheared, for example due to an increased wall section thickness. It is desirable to reduce the thickness of the ram arms to provide clearance for the increased effective diameter of the pipe prior to shearing while minimizing the overall form factor of the ram blocks. However, the ram arms experience high loads and reducing the thickness of the ram arms may result in an unacceptable amount of yielding or vertical separation from one another, possibly leading to failure of the BOP.